In conventional gear checking systems, a workpiece gear which has been machined with gear teeth on its periphery is tested for deviations of the machined surfaces within a predetermined tolerance range. In one widely-used form of gear checking system, a master gear which has been precisely machined is mounted on an arbor, and a workpiece gear 12 is brought into engagement with it on a spring-loaded slide. The master gear is then slowly turned by hand, and the displacements of the workpiece gear along the axis of the slide are measured on a gauge to determine whether deviations of the center distance between the master and workpiece gears lie within an acceptable tolerance range.
As illustrated in FIG. 3, such conventional gear checking systems have the problem that slight inaccuracies are introduced when the master gear 10 is turned manually by the operator. The arbor shaft 11 of the master gear usually has a slight clearance T.sub.0, of the order of 0.0003 inch, for a metal-to-metal fit of the master gear thereon. When the operator applies a turning force in the tangential direction B with the palm of the hand to the master gear 10, a pushing force in the radial direction A or a pull in the tangential direction B may be directed on the master gear, which can result in erroneous displacements of the workpiece gear along the slide axis S through the clearance T.sub.0 of the arbor shaft 11, or through friction between the master gear and the arbor shaft.
Thus, errors will be introduced into the measurement of the workpiece gear affecting the reliability of the measurement. Since manual turning of the master gear through 360 degrees requires repeated application of force by hand, the errors are repeated further and the checking time is increased. Moreover, the conventional system can be unsafe since the operator's hand might become caught in the area between the two gears. Motor drives have been employed to turn the master gear, but they can introduce vibrations into the measurement and are more expensive to produce. Such motor drives are engaged with a spindle through a drive belt or use a live spindle.
Therefore, it is a principal object of the invention to provide a gear turning assembly for a gear checking system which can be operated without introducing errors into the workpiece tolerance measurements. It is a further object to provide a master gear turning assembly which is inexpensive and simple in construction and can be easily retrofitted onto existing gear checking systems in wide use. It is further desired to provide an assembly which has improved safety features and advantages in terms of convenient operation either manually or with a motor drive.